1. Field of the Invention
This invention relates to positioning of sheets in a feed path. It particularly relates to positioning sheets of paper in a feed path for subsequent processing such as electrophotographic reproduction.
2. Description of the Related Art
Conventional sheet aligning mechanisms for equipment using paper feed stocks, such as electrophotographic reproduction equipment, use crossed nip rollers in conjunction with fixed guides and gates for positioning paper. Such systems commonly use sheet driving rolls which push the sheets against such guides and gates. These conventional systems have many drawbacks. If the guide and gate surfaces with excessive force, the edges of the sheets can be bent or crumpled. This condition occurs especially with lightweight papers and causes problems in downstream feeding of the paper. Thus, each system must be carefully set up for a narrow range of paper weight to provide sufficient drive force for movement of the sheet without damaging the sheet as it is driven against a guide or gate. In addition, undesirable dust is formed as a result of the impact and sliding of the paper against the hard guide surfaces. Further, duplex copying requires an additional station to shift the sheet laterally before it is returned to the cross roll feeder for re-feeding, so that the sheet can be realigned by the cross roll feeder against the guide. In addition, such systems are prone to drive roll slippage which can cause misregistration and smearing.
Sheet guide systems for shifting the lateral position of the guide have been proposed and are shown in U.S. Pat. Nos. 4,799,084 and 4,805,892. However, these systems do not provide for skew adjustment of the sheet and do not gate the sheet for downstream operations.
Belt-type feeders with variable edge distancing have been proposed for providing skew correction of sheets. Such designs are shown in U.S. Pat. Nos. 3,754,826 and 4,082,456. However, such arrangements do not provide precise lateral and longitudinal positioning of the sheet.
Sheet aligners without guides, using drive rollers for sheet alignment have also been proposed. One such design is disclosed in U.S. Pat. Nos. 4,438,917 and 4,511,242. However, this design has several drawbacks including the need for initially feeding sheets at a significant skew angle to the aligning rolls and sensor system. This unduly complicates the feeding system and requires a longer feed path to achieve sheet alignment. This has an adverse effect on the speed at which the aligner can perform its function and limits its capacity. In addition, the longer feed path results in an overall increase in the size of the equipment. Further, the electronic control systems required for this design are relatively complex and costly.